Se Bond Lengths Research Articles

Synthesis, Conformation, and Metabolism of a Selenium Bilirubin

A symmetrical C(10)-selena-bilirubin analog, 8,12-bis(2-carboxyethyl)-7,13-dimethyl-2,3,17,18-tetraethyl-10-selenabiladiene-ac-1,19(21H,24H)-dione was synthesized from 8-(2-carboxyethyl)-2,3-diethyl-7-methyl-(10H)-dipyrrin-1-one in one step by reaction with diselenyl dichloride. The selena-rubin exhibited UV-vis and NMR spectroscopic properties similar to those of the parent mesobilirubin, and like bilirubin and mesobilirubin, it adopts an intramolecularly hydrogen-bonded conformation, shaped like a ridge-tile but with a steeper pitch. The longer C–Se bond lengths (2.2 A) and smaller bond angles at C–Se–C (88°), as compared to C–CH2–C (∼1.5 A, ∼106°), lead to an interplanar angle between the two dipyrrinones of only 72°, which is considerably less than that of bilirubin (∼100°) and close to that (74°) of its 10-thia-rubin analog. Despite the conformational distortion, the sensitivity of Se toward oxidation and the typically weak C–Se bond, the selena-rubin is metabolized in normal rats, like bilirubin, to acyl glucuronides, which are secreted into bile. In mutant (Gunn) rats lacking bilirubin glucuronosyl transferase (UGT1A1), glucuronide or other metabolites of the selena-rubin were not detected in bile, demonstrating the importance of hepatic glucuronidation for its biliary excretion.

Synthesis and characterization of chalcogenoic aminophosphines: X-ray structures of Bu t2P(E)NHPr n (E=Se, Te), Ph 2P(Se)NHPr n and {Et 2P(Se)} 2NPr n

The four title compounds have been synthesized and characterized by 1H, 13C and 31P NMR spectroscopy and their identities confirmed by elemental analysis and X-ray crystallography. Bu t 2P(E)NHPr n [E=Se ( 1); E=Te ( 2)] and Ph 2P(E)NHPr n [E=Se ( 3)] were prepared by the metathesis reaction of LiNHPr n with the appropriate chlorophosphine in diethylether at −78 °C, followed by reaction with elemental selenium or tellurium at reflux temperatures. ( 1) and ( 2) are isostructural with PSe 2.1163(14) Å and PTe 2.3642(13) Å. In ( 3) a PSe bond length of 2.1159(10) Å is observed. ( 4) was prepared by the additional of two equivalents of diethylchlorophosphine to the dilithium salt of n-propylamine.

Raman band of matrix isolated Na MSe N clusters

Selenium clusters are doped with sodium atoms in the reaction zone of a dual laser vaporization source. Product clusters Se N and Na 2Se N with N=4–8 are deposited in a nitrogen matrix and investigated by Raman spectroscopy. Beside the Raman band of pure Se N clusters, a new intense band between 165 and 225 cm −1 is observed. Within a simple model of dynamical charge transfer the new band is attributed to certain vibrational modes with considerable changes of Na–Se bond lengths. The assignment is confirmed by density functional calculations. A bonding model for the Na 2Se N clusters containing horseshoe shaped polyanionic selenium chains is developed.

Theoretical analysis of microscopic strain distribution and phase stability of Zn chalcogenide alloys using valence force field model

Microscopic strain distribution in II–VI–O alloy systems is theoretically analyzed using the valence force field model. ZnSeO and ZnSO alloys have a maximum strain energy at O composition of 50% due to a large lattice mismatch between constituting materials. Zn–Se bond length decreases with increasing O composition and Zn–O bond increases with decreasing O composition. Se atoms rather than O are easier to move in order to reduce strain energy because of the small elastic constant of ZnSe compared with ZnO. The lattice deformation occurs mainly at tetrahedra containing O–Zn–Se bonds with Zn atom in the center.

Synthesis and crystal structure of hexahydrobis[(1,3-p-dimethylaminobenzyl)-1,3-diazepine]-2-selenone, C23H32N4Se.

In the title compound, C23H32N4Se, was synthesized and its crystal structure was determined by single crystal X-ray diffraction. The compound crystallizes in orthorhombic system, space group Pbca, a = 10.9960(10)A, b = 14.9460(9)A, c = 27.565(5)A and Z = 2. According to X-ray crystallographic studies, the diazepine ring is observed to be in a disordered state. The site-occupancy of the major compenent refined to 0.53(1). The C=Se bond length of 1.862(4)A is a double bond character. The dihedral angle between the two phenyl rings is 37.7(2) degrees.

Effect of pressure on structural properties and energy band gaps of γ‐InSe

AbstractWe have investigated theoretically the effect of hydrostatic pressure on interatomic bond lengths and energy band gaps of γ‐InSe. Total energy calculations were performed using the linear augmented plane wave (LAPW) method, taking into account scalar relativistic corrections as well as spin‐orbit coupling. Internal structural parameters were optimized for different pressures by adopting as input the unit cell parameters known from experiment. Our theoretical results for the nearest‐neighbor In–Se bond length are in excellent agreement with a recent experimental determination from high‐pressure EXAFS measurements. The covalent In–In bond is found to be more compressible than the partially ionic In–Se bond. We also present the calculated pressure dependence of band gaps and compare to recent high‐pressure experimental studies of optical and transport properties. A large negative pressure coefficient is obtained for the indirect Z–A gap. This leads to a crossover from a direct to an indirect fundamental gap within the stability range of the γ‐polytype of InSe, in qualitative agreement with recent experiments.

Structure of amorphous Ge xSe 1− x and Ge xSe yZn z thin films: an EXAFS study

Extended X-ray absorption fine structure (EXAFS) measurements have been made on thin films of a-Ge x Se 1− x with 0.2< x<1. The results show that the Ge–Ge, Ge–Se and Se–Se bond lengths have values 2.45, 2.37 and 2.32 (all ±0.03) Å, respectively and are independent of film composition. The partial atomic coordination numbers of Ge and Se suggest that the films have a predominantly chemically ordered 4-2 coordinated covalent bond network structure throughout the whole composition range, as found by others for Ge–Se bulk glasses with x<0.4. EXAFS data for a-Ge x Se y Zn z films show that the lengths of Ge–Zn and Se–Zn bonds are 2.57±0.05 and 2.44±0.03 Å, independent of the composition. Results on the atomic coordinations reveal that Zn is fourfold coordinated and preferentially bonds to Se atoms.

Tris(tert-butyl)phosphine selenide, the missing link in tris(tert-butyl)phosphine chalcogenide structures (t)Bu(3)P==X (X = O, S, Se, Te).

In tris(tert-butyl)phosphine selenide, C(12)H(27)PSe, all the methyl ligands are disordered over two sites in the ratio 70/30. The molecule displays crystallographic C(3) symmetry. The bond angles at the P atom are distorted tetrahedral [C--P--C 110.02 (5) degrees and Se==P--C 108.91 (5) degrees ]. The P--C and P==Se bond lengths are 1.908 (1) and 2.1326 (6) A, respectively. A comparison of the structural data of the complete series of tris(tert-butyl)phosphine chalcogenides ((t)Bu(3)PO, (t)Bu(3)PS, (t)Bu(3)PSe and (t)Bu(3)PTe) with the corresponding data of other phosphine chalcogenides substituted by smaller organic groups shows the great influence of the bulky tert-butyl ligands.

The First Kinetically Stabilized Germanethiones and Germaneselones: Syntheses, Structures, and Reactivities

The first kinetically stabilized germanethiones (germanium−sulfur double-bond species) and germaneselones (germanium−selenium double-bond species) were synthesized. Dechalcogenation of the novel 1,2,3,4,5-tetrachalcogenagermolane Tbt(Tip)GeX4 (Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, Tip = 2,4,6-triisopropylphenyl, X = S or Se) with 3 molar equiv of triphenylphosphine gave diaryl-substituted germanethione Tbt(Tip)GeS 1a and germaneselone Tbt(Tip)GeSe 2a as orange−yellow crystals and red crystals, respectively, which were unstable in air but thermally quite stable. Chalcogenation of germylene Tbt(Dis)Ge: resulted in the isolation of the corresponding germanethione Tbt(Dis)GeS 1b and germaneselone Tbt(Dis)GeSe 2b (Dis = bis(trimethylsilyl)methyl). The molecular structures of germanethione 1a and germaneselones 2a,b determined by X-ray crystallographic analysis indicate that they have trigonal planar geometies around the germanium atom and a remarkably shorter Ge−S (2.049(3) Å for 1a) or Ge−Se bond lengths (2.180(2) Å for 2a and 2.173(3) Å for 2b), compared with that of typical single bonds. The double-bond characters are also reflected in their spectral data such as UV/vis (1a, 450 nm; 1b, 432 nm; 2a, 519 nm; 2b, 492 nm), Raman (1a, 521 cm-1; 1b, 512 cm-1; 2a, 381 cm-1; 2b, 386 cm-1), and 77Se NMR (2a, 941 ppm; 2b, 872 ppm). The germanethiones and germaneselones underwent [2 + 2] (with phenyl isothiocyanate), [3 + 2] (with mesitonitrile oxide), and [4 + 2] cycloadditions (with 1,3-dienes) to give the corresponding adducts in high yields. The regioselectivities of the [4 + 2] cycloadditions were examined using unsymmetrical dienes such as isoprene and interpreted in terms of the interaction between LUMO of the GeX unit and HOMO of the diene part.

Isolated Se6Rings in the Voids of a Weakly Interacting, Electroneutral, and Crystalline SiO2Matrix: Combined Experimental and Theoretical Study

For the first time a selenium species has been successfully trapped in the voids of an electroneutral SiO2 modification, namely, in the porosil decadodecasil 3R (DDR). Raman spectroscopy in combination with theoretical ab initio calculations at the SCF and MP2 levels of theory have been used to assign the observed spectral bands exclusively to Se6 rings with D3d symmetry. The A1g(r) and Eg(r) mode frequencies of the matrix-isolated Se6 rings are considerably higher than those of bulk Se6, suggesting that intermolecular correlations are lost for the perfectly isolated molecules in the microporous host matrix. By an EXAFS analysis of Se K-spectra, Se−Se bond lengths of 2.34 Å and next-nearest Se···Se distances of 3.61 Å are obtained, in very good agreement with the theoretical ab initio studies. EXAFS analysis in addition reveals that the interaction between the SiO2 framework and the embedded Se6 rings are weak, resulting in a novel host−guest compound with nearly unperturbed Se6 guest molecules. The crystalline electroneutral host thus acts similarly to a noble gas matrix at low temperatures.

X-ray Diffraction Study of the Crystal Structure of the Tl Ternary Chalcogenides Tl2x In2(1−x)Se2, x = 0.2, 0.3,...0.9

A series of thallium ternary chalcogenides with the composition Tl2x In2(1−x)Se2, x = 0.2, 0.3,...0.9, have been studied by X-ray powder and, for some of them, single-crystal diffraction. They are tetragonal, space group I4/mcm, Z = 4, and isostructural with the binary semiconductor TlSe. Their crystal structures have been solved by direct methods and refined by the Rietveld method to a precision which is satisfactorily comparable to single-crystal results. As x is changed from x = 0.2 to x = 0.9 the unit-cell parameters and volume decrease or increase following Kurnakov's law, which is valid for solid solutions. Refined positional parameters of Se, In—Se and Tl—Se bond lengths vary with x also according to the same law. The distribution of In and Tl cations in 4(a) and 4(b) sites depends on the stoichiometry x and the crystals are composed of [In3+Se2]_{\infty}^- chains along the c axis in which InSe4 tetrahedra share edges; the chains are interconnected with Tl+(In+) ions.

Molecular and crystal structure of 1-methylmorpholinium 6-methyl-4-phenyl-3-cyano-5-ethoxycarbonyl-1,4-dihydro-2-pyridineselenolate

The structure of 1-methylmorpholinium 6-methyl-4-phenyl-3-cyano-5-ethoxycarbonyl-1,4-dihydro-2-pyridineselenolate was studied using x-ray diffraction analysis. It was found that the 1,4-dihydropyridine ring has a boat conformation, and the plane of the pseudoaxial phenyl substituent is perpendicular to the bottom of this boat. In the anion, the C−Se bond length, which is 1.882(2) A, indicates that the negative charge is formally located on the Se atom. The anions and cations of the salt in the crystal are linked by intermolecular hydrogen bonds.

Na 5AuSe 12-the first selenoaurate(III) with discrete complex anions

The novel polyselenoaurate(III) Na 5AuSe 12 was prepared by reacting a stoichiometric mixture of Na 2Se, Au and Se at 345°C followed by slow cooling. Na 5AuSe 12 forms transparent red crystals of lamellar habit. It is monoclinic, m P36, s.g. P2 1, with a=7.145(1) Å, b=16.790(6) Å, c=8.291(1) Å, β=107.13(1)°, Z=2. The crystal structure was determined from diffractometer data and refined to a conventional R of 0.032 (3830 F o's, 163 variables). Na 5AuSe 12 contains discrete mononuclear anions [AuSe 12] 5− which are formed by four triselenide chains in end-on coordination with the central atom. The Au-atom is in an almost undistorted square planar coordination through Se. The mean Au–Se bond length is 2.500 Å, Se–Se bond lengths in the Se 3−chains are in the range of 2.346–2.363 Å. The shortest intra-anionic Se–Se-contacts are in the range of 3.19–3.27 Å. In the crystal structure the [AuSe 12] 5− anions are stacked in columns along [100]. Together with three of the five crystallographically independent Na +-ions the columns are arranged in slabs parallel to (010)-plane which are separated by layers of the remaining Na +-ions. Na 5AuSe 12 is the first alkali selenoaurate(III) containing molecular anions. It undergoes peritectic decomposition at 275°C and is soluble in dimethylformamide.

From Organometallic Selenolates to Organoselenolato Complexes of Mo, W and Mn

Organometallic selenolates of Mo, W and Mn can be easily obtained via insertion of selenium into the alkali-metal transition-metal bonds of appropriate carbonylates. Subsequent reactions with various organic electrophiles lead to the corresponding organoselenolato complexes. X-ray structure analyses afforded M - Se bond lengths consistent with the presence of single bonds. 77Se NMR studies were performed to determine electronic influences of the organoselenolato function.

Raman and X-ray absorption study of selenium incorporated into the channels of mordenite: Dependence on the ion exchange and the method of incorporation

Influence of ion exchange and method of selenium incorporation into mordenite channels on the structure of incorporated selenium species are studied by Raman and X-ray absorption spectroscopy. It is shown that Se chains prepared by Se vapor adsorption are more regular than Se chains prepared by pressure injection of liquid Se. Concentration ratio between Se chains and Se 6 rings is found to be practically independent of the method of preparation but dependent on the type of cations in mordenite channels. Substitution of Na cations by larger monovalent cations leads to a decrease in Se chains concentration compared to Se 6 rings concentration and to an increase in average SeSe bond length. X-ray absorption spectrum of M-Se for polarization of radiation perpendicular to the channels is shown to be determined mainly by Se6 rings, and that for polarization parallel to the channels is a superposition of the absorption of chains and rings. Selenium incorporated into H-form of mordenite is found to be located not only in the original mordenite channels, but also in meso-channels organized due to partial destruction of the interchannel walls.

Structural and electronic properties of Ga2Se3

We study the defect tetrahedral semiconductor Ga2Se3 with ordered vacant sites using state-of-the-art density-functional calculations. The calculated main structural properties (the average cubic lattice parameter, a0=10.20 a.u., and the average Ga–Se bond length, r=4.52 a.u.) and electronic properties (the forbidden energy gap, direct, which amounts to about 2.4 eV) are in good agreement with the experimental data. The role of the coordination defects is analyzed in detail, and the contribution of the different atoms to the electronic density of states is also discussed. No significant differences are found if the vacant sites are ordered according to a monoclinic structure rather than orthorhombic, both previously proposed in literature, since the peculiar features of the structural and electronic properties are strongly related to the vacancies and their local environment rather than to their particular ordering. We also discuss the results obtained for the orthorhombic phase pseudomorphically grown on GaAs or ZnSe(001) substrates.

The Reaction of Potassium Polyselenides with [CpW(CO)3Cl] in DMF - Formation and Crystal Structure of [CpW(CO)3SeC(O)NMe2] and {[CpW(CO)3]2Se4}

The reactions of the potassium polyselenides „K2Se6” and „K2Se8” with [CpW(CO)3Cl] and 18-crown-6 in DMF lead to a mixture of the selenido complexes {[CpW(CO)3]2Se4} 1 and [(18-crown-6)K]+[CpW(Se4)2]−3 and the Se−bonded selenocarbamato complex [CpW(CO)3SeC(O)NMe2] 2 in yields depending on the selenium content of the used potassium polyselenides („K2Se6” or „K2Se8”). A similar reaction in THF produces {[CpW(CO)3]2Se4} as the main product. X-ray structures of 1 and 2 were determined. In 1 the Se4-chain is bonded in a μ2-η1 fashion, with corresponding W−Se bond lengths of 264.0(1) and 264.3(1) pm. The Se−Se bond lengths lie in the range 232 to 237 pm. The first example of an η1 Se-bonded selenocarbamato ligand is observed in the crystal structure of 2, with a W−Se bond length of 263.1(1) pm. The 77Se-NMR data are compared with the corresponding data of related complexes.

From Organometallic Selenolates to Organoselenolato Complexes of Mo, W and Mn

Organometallic selenolates of Mo, W and Mn can be easily obtained via insertion of selenium into the alkali-metal transition-metal bonds of appropriate carbonylates. Subsequent reactions with various organic electrophiles lead to the corresponding organoselenolato complexes. X-ray structure analyses afforded M - Se bond lengths consistent with the presence of single bonds. 77Se NMR studies were performed to determine electronic influences of the organoselenolato function.

Organometallic Selenolates. VII. (Benzylselenolato-Se)tricarbonyl(η5-cyclopentadienyl)molybdenum(II) and Bis[1,2(η5)-cyclopentadienyl]-di-μ-ethylselenolato-di-μ-selenido-dimolybdenum(IV)(Mo—Mo)

Compound (1), [Mo(η5-C5H5)(C7H7Se)(CO)3], is monomeric in the solid state. The Cp(CO)3MoSe moiety (where Cp is cyclopentadienyl) displays a `piano-stool' arrangement with an Mo—Se bond length of 2.6294 (4) Å and an essentially ideal tetrahedral bond angle at selenium [109.74 (8)°]. The binuclear compound (2), [Mo2(η5.C5H5)2(C2H5Se)2(Se)2], consists of linear cp–Mo–Mo–Cp moieties with Mo=Mo double bonds, which are quadruply bridged by two pairs of selenido and ethylselenolato ligands.

An X-ray absorption study of selenium confined in channels of cancrinite: Evidence for dimerisation in highly oriented chains

Local structure of one-dimensional selenium chains in cancrinite channels have been studied by polarised X-ray absorption. Polarised EXAFS reveals that selenium atoms are one-fold coordinated and well-aligned along the c-axis of cancrinite. The obtained SeSe bond length is 2.40 ± 0.01 A ̊ . The results provide direct evidence for dimerisation of selenium chains and suggest incommensurate intercalation of dimers which do not form a triplet (π-bond) state or a dangling bond state. Highly anisotropic polarisation dependence of XANES demonstrate that antibonding 4p(σ ∗) states are partially filled suggesting a charge transfer from Na cations located in the channels.